1. Field of the Invention
This invention relates generally to the field of solenoids and solenoid actuated valves. More specifically, it relates to a solenoid of improved construction which has increased pulling capacity compared with prior art solenoid constructions.
2. Prior Art
Solenoids and solenoid actuated valves are well-known in the art. Typically the solenoid comprises a helically wound coil of insulated wire capable of inducing a directionalized magnetic field when an electric current flows through the coil. The solenoid may be equipped with a movable plunger in the form of an iron rod or bar designed for axial movement with respect to the coil.
The force or pull which may be exerted by the solenoid is a function of the current in the coil once the core has become saturated. Prior to saturation, force or pull is proportional to the square of the exciting current. In general, the force or pull of a solenoid may be increased using an ironclad solenoid so as to provide an iron return path for the magnetic flux. As a corollary, it is well-known that as the air gaps in the magnetic circuit decrease the force or pulling power of the solenoid increases. Thus, in the conventional plunger type solenoid, as the plunger or armature moves axially into the coil, the air gap in the magnetic circuit decreases and the force or pull of the solenoid increases.
Typically, the solenoid and armature will have both a primary and a secondary air gap. These gaps will usually be found at opposite ends of the armature and will be of the same magnitude since the solenoid is ordinarily designed to provide essentially no air gap in the fully energized state. The useful travel of the armature is thus equal to approximately half of the total initial air gap.
In place of the plunger type of armature referred to above, the armature may be mounted on a rod or bar which, in turn, is journalled for reciprocating movement within the solenoid coil as shown in U.S. Pat. Nos. 2,765,808 and 3,250,293. Such movement may be resisted by frictional forces caused by the side thrust of the armature or the plunger bar which is drawn against the inside surface of the solenoid coil by the magnetic field.
A modification of the plunger type of armature is shown in U.S. Pat. No. 1,333,681 where a cup-shaped armature restrained to move only in an axial direction acts upon a rod passing through the solenoid coil. A further modification of the plunger type of armature appears in U.S. Pat. No. 3,325,139 wherein the armature has a tapered or conical shape and moves axially into a mating portion of the core piece. A sliding annular armature constrained to move in an axial direction is shown in U.S. Pat. Nos. 3,422,850 and 3,523,556. A pivotally-mounted, spring-loaded armature functioning as a valve disc is shown in U.S. Pat. No. 3,751,001. The armature or valve disc is restrained by the pivotal mounting to an oscillation or oscillatory motion about the pivot mounting.